This application is the national phase of international application PCT/JP99/02771 filed May 26, 1999 which designated the U.S.
The present invention relates to a muffler.
As a conventional internal combustion engine muffler, a muffler has been generally employed which is, as shown in FIG. 7, constituted by dividing a main body formed of a shell 101 and outer plates 102, 103 into expansion chambers 106, 107 and a resonance chamber 108 by inner plates 104, 105. Furthermore, the muffler is constituted of an inlet pipe 109 for introducing exhaust gas, an outlet pipe 110 for discharging the exhaust gas to the atmosphere, and an inner pipe 111 for connecting the respective chambers to each other.
Moreover, as shown as the outer plates 102, 103 and inner plates 104, 105 in FIGS. 7, 8A and 8B, it is known that connection holes 112 for passing the respective pipes are formed in a flat plate molded by press processing, and linear ribs (beads) 114 are formed in a plane portion 113 excluding the connection holes 112, so as to restrain surface vibration of the outer plates 102, 103 and inner plates 104, 105, and to prevent abnormal noise and breakage caused by the surface vibration.
In the outer plates 102, 103 and inner plates 104, 105, since the plane portion 113 except the ribs 114 is formed in a broad range, in parallel and opposite arrangement of these plates, a high frequency component of the exhaust noise is reflected to the broad plane portion 113 to reciprocate many times between the opposite plates. Therefore, with respect to the exhaust noise with a specified frequency, sharp resonance occurs, reverberation time is lengthened, and further a flutter echo phenomenon occurs, which causes a secondary noise in the muffler.
Moreover, when the rib 114 is linearly formed as described above, diffused reflection of exhaust noise occurs in a direction perpendicular to a linear direction of the rib 114, but no irregular reflection occurs in the linear direction. Therefore, the reflected high frequency component of exhaust noise fails to sufficiently interfere with each other, and secondary noise is insufficiently restrained.
Therefore, an object of the present invention is to provide a muffler in which by enhancing vibration-damping effects of outer and inner plates, and by effectively utilizing a limited plate area to form many irregular reflection elements, the exhaust noise can be reduced as compared with the aforementioned conventional plate.
In order to attain the aforementioned objects, according to the present invention, there is provided a muffler in which an inside is divided into a plurality of chambers by at least an inner plate, a plurality of dot-shaped convex and concave portions are provided in at least one of the inner plate and the outer plate, the convex portions and the concave portions are alternately arranged to be surrounded with one another, and the convex portion is connected to the concave portion by a curved surface.
In the present invention, since high frequency components of the exhaust noise having hit the dot-shaped convex and concave portions are diffusely reflected to interfere with each other in all spatial directions, the secondary noise is restrained, and the exhaust noise is reduced as compared with the conventional art. Furthermore, since the convex and concave portions are alternately disposed and connected to each other by the curved surfaces, plate surface rigidity is enhanced, and abnormal noise and breakage by plate vibration can also be prevented.
Moreover, in the present invention, the convex and concave portions may be disposed substantially on the entire surface of the plate.
Thereby, the aforementioned irregular reflection is performed substantially on the entire surface of the plate, and the exhaust noise is further reduced.
Furthermore, in the present invention, a burring portion for passing a pipe can also be disposed on the convex or concave portion.
Pipe vibration is restrained by providing the burring portion without deteriorating the plate surface rigidity.
Moreover, in the present invention, the convex and concave portions may be provided on the outer and inner plates disposed opposite to each other or the inner plates disposed opposite to each other.
By disposing the plates with the convex and concave portions disposed thereon opposite to each other, the aforementioned reduction effect of the exhaust noise is further enhanced.